Cleanup PreferenceMACs on browser_tests startup

chrome/test/base/chrome_test_launcher.cc

Index: chrome/test/base/chrome_test_launcher.cc
diff --git a/chrome/test/base/chrome_test_launcher.cc b/chrome/test/base/chrome_test_launcher.cc
index a6e39530d5e307530e1de9bd951a0a9369f1db67..d83f87d3d44571beb0f4defbd896fac04e1c9e1d 100644
--- a/chrome/test/base/chrome_test_launcher.cc
+++ b/chrome/test/base/chrome_test_launcher.cc
@@ -52,7 +52,9 @@
 #endif
 
 #if defined(OS_WIN)
+#include "base/win/registry.h"
 #include "chrome/app/chrome_crash_reporter_client_win.h"
+#include "chrome/install_static/install_util.h"
 #endif
 
 ChromeTestSuiteRunner::ChromeTestSuiteRunner() {}
@@ -96,6 +98,21 @@ ChromeTestLauncherDelegate::CreateContentMainDelegate() {
   return new ChromeMainDelegate();
 }
 
+void ChromeTestLauncherDelegate::PreShardingCleanup() {
+#if defined(OS_WIN)
+  // Pre-test cleanup for registry state keyed off the profile dir (which can
+  // proliferate with the use of uniquely named scoped_dirs):
+  // https://crbug.com/721245. This needs to be here in order not to be racy
+  // with any tests that will access that state.
+  base::win::RegKey key(HKEY_CURRENT_USER,
+                        install_static::GetRegistryPath().c_str(),
+                        KEY_SET_VALUE | KEY_QUERY_VALUE);
+  if (key.Valid()) {
+    key.DeleteKey(L"PreferenceMACs");

[jam, 2017/05/17 19:06:16]

does this mean that if someone runs official browser_tests, it will delete this
key for the chrome that the use? that seems bad?

can we only delete the subkeys that have "scoped" in them?

[gab, 2017/05/17 20:01:05]

Yes, but it's not that bad (discussed details offline)
We could but that'd increase complexity where I don't think it's worth it.

+  }
+#endif
+}
+
 int LaunchChromeTests(int default_jobs,
                       content::TestLauncherDelegate* delegate,
                       int argc,